Developmental and regulatory aspects of prolactin (PRL) and growth hormone (GH) gene expression will be studied in normal mice and in two non-allelic dwarf mutants exhibiting phenotypic anomalies in PRL and GH production. The proposed experimental model will utilize intact glands and monolayer cultures of dispersed cells obtained from fetal and postnatal pituitaries of normal and mutant mice. (1) We will first establish the normal pattern of the onset of PRL and GH synthesis and analyze the response of normal pituitaries to estrogenic and glucocorticoid hormones. (2) We will next investigate whether dwarf pituitaries are able to synthesize, store or secrete either normal or defective PRL and/or GH at any stage in their development. These experiments will involve pulse labeling of organ and cell cultures, electrophoresis of the cell extracts on two dimensional gels, and fluorography. (3) Prolactin and GH synthesis and secretion will be quantitated by immunoprecipitation of labeled cell products and culture media using homologous antisera. (4) Prolactin and GH cells will be identified by immunocytochemistry with peroxidase labeled antibody. (5) The presence of the PRL and GH genes in dwarf mice will be ascertained by hybridization of mouse liver DNA to labeled cDNA prepared from rat PRL and GH mRNA. (6) The presence of nuclear and/or cytoplasmic PRL and GH mRNA in dwarf pituitary cells will be investigated by in situ hybridization of PRL and GH mRNA to labeled cDNA and autoradiography. (7) Physiological modulators of PRL and GH synthesis will be added to pituitary cultures and their effect on the development and maintenance of PRL and GH cell function will be assessed.